Vidaara.orgClass 11 · Physics
CodeVID-P11-04-NEW-01
Newton's Laws & Inertia — Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
Newton's first law is also called the law of:
- A.gravitation
- B.inertia
- C.momentum
- D.friction
2.
A force of 10 N on a 2 kg mass gives an acceleration of:
- A.$2\ \text{m/s}^2$
- B.$5\ \text{m/s}^2$
- C.$10\ \text{m/s}^2$
- D.$20\ \text{m/s}^2$
3.
The mathematical form of Newton's second law in terms of momentum is:
- A.$\vec{F}=m\vec{v}$
- B.$\vec{F}=\frac{d\vec{p}}{dt}$
- C.$\vec{F}=\frac{\vec{p}}{t}$
- D.$\vec{F}=\vec{p}t$
4.
During free fall in a lift, a person's apparent weight is:
- A.$mg$
- B.$2mg$
- C.zero
- D.$\frac{mg}{2}$
5.
Action and reaction forces act on:
- A.the same body
- B.different bodies
- C.no body
- D.the ground only
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
State Newton's first law of motion.
7.
A 6 kg body experiences a net force of 18 N. Find its acceleration.
8.
Why do passengers lurch backward when a bus suddenly starts?
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
A 70 kg person stands in a lift accelerating upward at $2\ \text{m/s}^2$. Find the apparent weight. ($g=10\ \text{m/s}^2$)
10.
Draw a free-body diagram of a block resting on a horizontal table and name the forces.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Derive $\vec{F}=m\vec{a}$ from $\vec{F}=\frac{d\vec{p}}{dt}$ for constant mass, and use it to find the force needed to accelerate a 1500 kg car at $3\ \text{m/s}^2$.
Answer Key
Section A — Multiple Choice Questions
- (B) inertia
- (B) $5\ \text{m/s}^2$
- (B) $\vec{F}=\frac{d\vec{p}}{dt}$
- (C) zero
- (B) different bodies
Section B — Short Answer (2 marks)
- A body remains at rest or in uniform motion in a straight line unless an external unbalanced force acts on it.
- $a=\frac{18}{6}=3\ \text{m/s}^2$.
- Inertia of rest: the body tends to stay at rest while the bus moves forward.
Section C — Short Answer (3 marks)
- $N=m(g+a)=70\times12=840\ \text{N}$.
- Two forces: weight $mg$ downward and normal reaction $N$ upward, with $N=mg$.
Section D — Long Answer (5 marks)
- $\vec{F}=\frac{d(m\vec{v})}{dt}=m\frac{d\vec{v}}{dt}=m\vec{a}$; $F=1500\times3=4500\ \text{N}$.
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